The present invention relates generally to a master cylinder in a hydraulic brake system for an automotive vehicle. More specifically, the invention relates to a tandem master cylinder having a primary piston and a secondary piston in tandem relationship and supplying the working fluid to front and rear wheel cylinders independently from each other.
The brake system master cylinder which has a primary piston for supplying working fluid to the rear wheel cylinders and a secondary piston for supplying the working fluid to the front wheel cylinders, has been known. In such a master cylinder, the primary piston and the secondary piston are positioned in the housing in tandem relationship so that they can be operated cooperatively by application of a brake pedal. As is well known upon applying the brake, the load applied to the front wheels is greater than that on the rear wheels, and, this phenomenon leads to what is known as the nose dive phenomenon. This causes locking of the rear wheels prior to locking of the front wheels and thus skidding of the vehicle. In the case of locking of the rear wheels prior to the front wheels, the vehicle tends to spin about the front wheels.
For preventing the vehicle from spinning caused by locking of the rear wheels, there has been developed brake systems having proportioning valves in the hydraulic circuit for the rear wheel brake system. This increases the cost for the brake system and makes the hydraulic circuit for the brake system so complicate that it is difficult to assemble and maintain.